Referring to FIG. 8, there is illustrated a configuration of a conventional dishwasher.
As shown in FIG. 8, dishwasher 801 has washer tub 802 therein, and water or warm water is supplied into washer tub 802 through water supply valve 803. Water drainage outlet 804 is disposed in the bottom portion of washer tub 802, and communicates with washing pump 805 driven by a motor for use in circulating wash water in washer tub 802. Further, strainer 806 for filtering particulate food debris from the wash water is installed in water drainage outlet 804.
Wash water supplied in washer tub 802 is suctioned by washing pump 805 through strainer 806 and is then directed into wash nozzle 807 disposed in the lower portion of washer tub 802 from washing pump 805. Once wash water has been sprayed by wash nozzle 807 onto soiled items 808 to be cleaned (kitchen and dining ware), it is circulated back to water drainage outlet 804 through a water passageway. At this point, solid food particulates removed from items 808 to be cleaned get to strainer 806 in wash water, and any debris too large to pass through strainer 806 are captured in strainer 806.
Further, heater 809 for heating wash water is disposed between wash nozzle 807 and the bottom portion of washer tub 802. Disposed above wash nozzle 807 is rack 810 for arranging items 808 to be cleaned therein in an orderly manner so they can be subjected to more effective spraying of wash water resulting in more efficient cleaning. Moreover, water drain pump 811 is for use in discharging wash water from dishwasher 801 via water drain hose 811a. Controller 812 controls electrical components such as water supply valve 803 and washing pump 805 (see, for example, Japanese Patent Laid-Open Application No. 2003-210378).
However, the conventional dishwasher having the above configuration shown in FIG. 8 is not capable of removing all types of food debris stuck on items 808 to be cleaned. Particularly, heavy or stubborn debris which are dried-on or baked-on stuffs remaining on kitchen ware items after preparing certain foods (e.g., gratin or savory steamed egg custard) cannot be removed by the conventional dishwasher.
To solve this problem, it has been proposed to add a pre-washing step to allow a detergent solution with a concentration higher than that for use in a normal washing operation to coat and remain on items 808 to be cleaned for a period of time. Adding this step improved the cleaning capability of the conventional dishwasher model, thereby enabling it to remove stubborn or heavy debris it could not before.
In this case, when using, for example, a mist generating device having an ultrasonic vibrator to promote coating of high concentration detergent solution on kitchen or dining ware items to be cleaned, food debris in wash water or mineral dissolved in water with high hardness, (e.g., ground or well water), may deposit and harden thereafter on the vibrating surface of the ultrasonic vibrator. Consequently, such deposits affect the operation of the ultrasonic vibrator by deteriorating its power considerably or causing it to malfunction.